Existing d-c motors, i.e. electric motors supplied by a d-c current, operate on the basis of commutation of current in conductors positioned within a magnetic field induced by alternatively oriented poles: The commutation of the current depending upon polarity of magnetic flux and direction of conductor movement is performed by means of a commutator, a mechanical device providing for switching between coils. Electric current is supplied to the commutator by means of carbon brushes. The d-c motor speed generally depends upon voltage and current running through the motor windings and is influenced by the load, i.e. by braking torque. The d-c motor speed can be easily controlled by changing the supply voltage and/or by excitation when the magnets are provided for by windings on salient poles. Necessary application of a commutator is a great disadvantage of known d-c machine constructions. Due to its construction and heavy mechanical stress, it needs regular maintenance and rather often exchange of the brushes. Sparking between the brushes and the commutator surface causes energy loss and electromagnetic interference. Development and progress in power electronics has resulted in gradual substitution of classic d-c machines by machines with electronic excitation of a rotating magnetic field. Current commutation either by a mechanical commutator or by electronic means represents also high men power and respective high material and labour costs. Magnetic poles made of permanent magnets simplify manufacturing process but are not suitable for all the applications and very often need gear-boxes.
It is an object of the invention to create a simple machine featuring simple regulation of direction and speed of rotation, low moment of inertia and simultaneously offering capability of installation within a relatively small area.
It is still a further object of the invention to create a machine featuring high long-term operational reliability without demands on maintenance during service.